Date: Thu, 18 Apr 2002 00:49:45 -0500 (CDT) From: Mike Silbersack <silby@silby.com> To: Mark Delany <markd@BushWire.Net> Cc: Bill Fenner <fenner@research.att.com>, <freebsd-net@FreeBSD.ORG> Subject: Re: What does FreeBSD do when listen queue is full ? Message-ID: <20020418004301.K17506-100000@patrocles.silby.com> In-Reply-To: <20020417213805.A91259@bushwire.net>
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On Wed, 17 Apr 2002, Mark Delany wrote: > Are we discussing what happens when the number of pending connections > exceeds the backlog? If the suggestion is to leave such connections > pending then the question becomes what's the real purpose of backlog? Yes, that is what we're discussing. > For arguments sake, say I have a web server that I know handles 10 > requests per second and I want to offer a 2 second response time. To > do this I set the backlog to 20 on each of the web servers and > configure the load balancer to periodically check each server by > attempting to establish a session. > > If the load balancer connection attempt fails then it knows that that > particular server already has 2 seconds worth of work so it should not > consider that server as available at the moment (note that some load > balancer configurations mean that connection counting is not possible > and, oftentimes they don't do so accurately anyway). Well, 4.5+ would already be considered broken by your standards; it does not send a RST when dropping connections that have exceeded the backlog. I understand your method, but it seems perhaps a bit too simplistic. Have you considered having the load balancer make a simple request (fetching a static piece of html) every .25 seconds or so? The total response time from such connections would presumably give you a much better picture of how loaded the server is. If we do go ahead and make the changes that Bill proposes, it should be possible to add a sysctl that would cause a RST to be emitted rather than the connection to be returned to the syncache. Mike "Silby" Silbersack To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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